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RE: seismic forces

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Chris,

Depending on your POV, Williams may even be better. As a talented but not bestselling SF/Fantasy author, Williams, unlike Mr. King, still gets edited...

(And I have read THE RIFT. Very well written.)

Gary

Gary J. Ehrlich, PE 
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-----Original Message-----
From: Christopher Wright [mailto:chrisw(--nospam--at)skypoint.com] 
Sent: Tuesday, November 25, 2008 12:08 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: seismic forces


On Nov 25, 2008, at 8:47 AM, Mike Jones wrote:

> Walter Jon Williams wrote a fictional account of a NM event  
> happening "Today".
Probably something like 'Lucifer's Hammer.' I used to read a lot of  
apocalyptic science fiction--if Williams is as good as _The Stand_  
(Stephen King) it'll be pretty damn good.

In a related vein, the statistical approach to earthquake occurrence  
give me serious heartburn. Nuke plants all have reams of SSE and OBE  
response spectra, including plants in Minnesota and Nebraska and  
other states with no particular seismic history. I play by the rules  
and use them as if they were revealed wisdom, but sometimes I wonder  
what the reality actually is. The whole process is so non-linear, I  
can't imagine that any two damaging earthquakes really have any  
similarity. The plates seem to move in the same relative direction,  
but the contact geometry must really change enormously over time and  
certainly during an earthquake. Tack on the discovery of new fault  
lines from time to time and the predictability must be very iffy.

The small quakes probably do repeat to a degree, but extrapolation of  
small quake behavior, which necessarily doesn't change much, to large  
quake response which can move river beds seems like a leap of faith,  
not science.

It really seems like a big stretch to pronounce a certain  
acceleration as having a '2%-in-50 chance of exceeding an M7.1 to  
M7.3 earthquake.' Statistical analysis of this sort demands a fairly  
large population of nominally similar members and a solid  
quantitative data base for numerical comparison. Damaging earthquakes  
just don't fit these requirements, especially the big ones like the  
Charleston and New Madrid quakes. We really can't determine when a  
future earthquake may occur, let alone how big it might be, simply  
because we only have so few examples. The idea of imposing some  
notion of a time element on the really damaging quakes, to quantify  
repetition seems far-fetched. The validity of a 2500 year event is  
nonsensical. Seems to me like the do-something-even-if-it's-wrong  
philosophy that we've all had to sweep up after.

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania  
1864)
http://www.skypoint.com/members/chrisw/



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